EP1079084A2 - Moteur à combustion interne - Google Patents

Moteur à combustion interne Download PDF

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Publication number
EP1079084A2
EP1079084A2 EP00117716A EP00117716A EP1079084A2 EP 1079084 A2 EP1079084 A2 EP 1079084A2 EP 00117716 A EP00117716 A EP 00117716A EP 00117716 A EP00117716 A EP 00117716A EP 1079084 A2 EP1079084 A2 EP 1079084A2
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EP
European Patent Office
Prior art keywords
amount
fuel ratio
combustion chamber
combustion
temperature
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP00117716A
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German (de)
English (en)
Other versions
EP1079084A3 (fr
EP1079084B1 (fr
Inventor
Shizuo Sasaki
Satoshi Iguchi
Toshiaki Tanaka
Shinya Hirota
Masato Gotoh
Kazuhiro Itoh
Takekazu Ito
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Toyota Motor Corp
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Toyota Motor Corp
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Publication date
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Publication of EP1079084A3 publication Critical patent/EP1079084A3/fr
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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F02D41/005—Controlling exhaust gas recirculation [EGR] according to engine operating conditions
    • F02D41/0057—Specific combustion modes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B47/00—Methods of operating engines involving adding non-fuel substances or anti-knock agents to combustion air, fuel, or fuel-air mixtures of engines
    • F02B47/04—Methods of operating engines involving adding non-fuel substances or anti-knock agents to combustion air, fuel, or fuel-air mixtures of engines the substances being other than water or steam only
    • F02B47/08—Methods of operating engines involving adding non-fuel substances or anti-knock agents to combustion air, fuel, or fuel-air mixtures of engines the substances being other than water or steam only the substances including exhaust gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
    • F02D41/029—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a particulate filter
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/30—Controlling fuel injection
    • F02D41/38—Controlling fuel injection of the high pressure type
    • F02D41/40—Controlling fuel injection of the high pressure type with means for controlling injection timing or duration
    • F02D41/402—Multiple injections
    • F02D41/405—Multiple injections with post injections
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B2275/00—Other engines, components or details, not provided for in other groups of this subclass
    • F02B2275/14—Direct injection into combustion chamber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/13—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories
    • F02M26/22—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories with coolers in the recirculation passage
    • F02M26/23—Layout, e.g. schematics
    • F02M26/28—Layout, e.g. schematics with liquid-cooled heat exchangers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Definitions

  • the present invention relates to a compression ignition type internal combustion engine.
  • an engine exhaust passage and an engine intake passage are connected to each other through an exhaust gas recirculation (hereinafter abbreviated to"EGR") passage so as to prevent or suppress generation of NOx, such that exhaust gas, or EGR gas, may be recirculated into the engine intake passage through the EGR passage.
  • EGR exhaust gas recirculation
  • the combustion temperature within the combustion chamber decreases as the amount of EGR gas increases, namely, the EGR rate (the amount of EGR gas / the amount of EGR gas plus the amount of intake air) increases.
  • the amount of NOx generated is reduced with a reduction in the combustion temperature, and therefore the amount of NOx generated is reduced with an increase in the EGR rate.
  • the EGR rate is conventionally set within a range that does not exceed the maximum permissible limit. While the maximum permissible limit of the EGR rate greatly varies depending upon the type of the engine and the fuel, it is generally within a range of about 30% to 50%. In conventional diesel engines, therefore, the EGR rate is controlled to about 30% to 50% at the maximum.
  • the EGR rate was conventionally considered to have the maximum permissible limit, the EGR rate was selected within the range that does not exceed the maximum permissible limit so that the amount of smoke generated is reduced to be as small as possible. However, even if the EGR rate is determined so that the amounts of NOx and smoke generated are minimized, there is a limit to reduction in the amount of NOx and smoke generated, and in fact substantial amounts of NOx and smoke are still generated in actual engine operations.
  • the temperature of the fuel and its surrounding gas is greatly influenced by the heat absorbing function of gas that is present around the fuel upon combustion thereof, and the temperature of the fuel and its surrounding gas can be controlled by adjusting the quantity of heat absorbed by the gas around the fuel, depending upon the quantity of heat generated upon combustion of the fuel.
  • the amount of unburned HC discharged from the combustion chamber is not large enough to increase the temperature of the particulate trapping device to a level at which the particulates can be burned. It is thus difficult to favorably burn particulates.
  • the object may be accomplished by an apparatus having the features of claim 1.
  • the temperature of the particulate trapping device can be rapidly raised to a level at which the particulates can be burned.
  • an exhaust gas recirculation system for recirculating exhaust gas discharged from the combustion chamber, into an engine intake passage, and the inert gas consists of the exhaust gas recirculated by the exhaust gas recirculation system.
  • Fig. 1 illustrates the whole system of an internal combustion engine of four-stroke, compression ignition type, to which the present invention is applied.
  • the internal combustion engine includes a main body 1 of the engine, cylinder block 2, cylinder head 3, piston 4, and a combustion chamber 5.
  • the engine further includes an electrically controlled fuel injection valve 6, intake valve 7, intake port 8, exhaust valve 9, and an exhaust port 10.
  • the intake port 8 communicates with a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to an air cleaner 14 via an intake duct 13.
  • a throttle valve 16 that is driven by an electric motor 15 is disposed within the intake duct 13.
  • the exhaust port 10 is connected to a particulate trapping device 18 via an exhaust manifold 17.
  • the particular trapping device 18 as shown in Fig. 1 incorporates a particulate filter 19 for trapping soot and other particulates contained in exhaust gas. While various types of particulate filters are known in the art, the particulate filter 18 as a typical example consists of a porous ceramic, honeycomb structure. To the particulate trapping device 18 is attached a differential pressure sensor 20 adapted for detecting a difference between the pressure sensed on the upstream side of the particulate filter 19 and that on the downstream side thereof.
  • An air-fuel ratio sensor 21 is disposed within the exhaust manifold 17, as shown in Fig. 1.
  • the exhaust manifold 17 and the surge tank 12 are connected to each other through an EGR passage 22, and an electrically controlled EGR control valve 23 is disposed within the EGR passage 22.
  • a cooling system 24 for cooling EGR gas that flows through the EGR passage 22 is located around the EGR passage 22. In the embodiment shown in Fig. 1, engine coolant is fed to the cooling system 24 so that the EGR gas is cooled by the engine coolant.
  • Each fuel injection valve 6 is connected to a fuel reservoir, or a so-called common rail 26, via a fuel supply pipe 25.
  • the fuel is supplied from an electrically controlled fuel pump 27 whose discharge amount is variable, into the common rail 26, and the fuel having been supplied into the common rail 26 is then supplied to each fuel injection valve 6 through a corresponding fuel supply pipe 25.
  • the common rail 26 is equipped with a fuel pressure sensor 28 for detecting the fuel pressure within the common rail 26. In operation, the discharge amount of the fuel pump 27 is controlled based on an output signal of the fuel pressure sensor 28 so that the fuel pressure within the common rail 26 becomes equal to a target fuel pressure.
  • An electronic control unit 30 consists of a digital computer, and includes a ROM (read only memory) 32, RAM (random access memory) 33, CPU (microprocessor) 34, an input port 35 and an output port 36, which are connected to each other via a bidirectional bus 31.
  • Output signals of the differential pressure sensor 20 and the air-fuel ratio sensor 21 are respectively transmitted to the input port 35 via corresponding AD converters 37, and an output signal of the fuel pressure sensor 28 is also transmitted to the input port 35 via a corresponding AD converter 37.
  • the particulate trapping device 18 is provided with a temperature sensor 29 for detecting the temperature of the particulate filter 19, and an output signal of the temperature sensor 29 is transmitted to the input port 35 via a corresponding AD converter 37.
  • a load sensor 41 that is connected to an accelerator pedal 40 operates to generate an output voltage that is proportional to the amount of depression L of the accelerator pedal 40, and the output voltage of the load sensor 41 is transmitted to the input port 35 via a corresponding AD converter 37.
  • a crank angle sensor 42 that generates an output pulse each time the crankshaft rotates 30°, for example.
  • the output port 36 is connected to the fuel injection valve 6, electric motor 15, EGR control valve 23 and the fuel pump 27, via respective drive circuits 38.
  • Fig. 2 shows changes in the output torque and changes in the discharge amounts of smoke, HC, CO and NOx in an experiment in which the air-fuel ratio A/F (the horizontal axis in Fig. 2) is varied by changing the opening of the throttle valve 16 and the EGR rate during low-load operations of the engine. It is understood from Fig. 2 that the air-fuel ratio A/F decreases as the EGR rate is increased in this experiment, and that the air-fuel ratio A/F is equal to or smaller than the stoichiometric air-fuel ratio ( ⁇ 14.6) when the EGR rate is equal to or greater than 65 %.
  • the amount of smoke generated by the engine starts increasing when the EGR rate reaches around 40% and the air-fuel ratio A/F becomes equal to about 30. If the EGR rate is further increased to thereby reduce the air-fuel ratio A/F, the amount of smoke generated rapidly increases, and reaches its peak. If the EGR rate is kept further increased so as to reduce the air-fuel ratio A/F, the amount of smoke is rapidly reduced, and becomes substantially equal to zero when the EGR rate is controlled to 65% or greater and the air-fuel ratio A/F is reduced down to around 15.0. Thus, almost no soot is produced. At this time, the output torque of the engine is slightly reduced, and the amount of NOx generated by the engine is considerably reduced, whereas the amounts of HC and CO generated by the engine start increasing.
  • Fig. 3A shows changes in the combustion pressure within the combustion chamber 5 when the largest amount of smoke is generated with the air-fuel ratio A/F being equal to about 21.
  • Fig. 3B shows changes in the combustion pressure within the combustion chamber 5 when the amount of smoke generated is substantially zero with the air-fuel ratio A/F being equal to about 18.
  • the amounts of HC and CO discharged from the combustion chamber increase as the amount of smoke generated, or the amount of soot generated, becomes equal to substantially zero.
  • hydrocarbon is discharged without turning into soot.
  • straight chain hydrocarbon or aromatic hydrocarbon contained in the fuel as shown in Fig. 4 thermally decomposes to form a precursor of soot as the temperature is raised with a lack of oxygen, and then soot is produced which mainly consists of a solid as an aggregate of carbon atoms.
  • soot is produced which mainly consists of a solid as an aggregate of carbon atoms.
  • the actual process of formation of soot is complicated, and the form taken by the precursor of soot is not clear.
  • HC discharged at this time is regarded as a precursor of soot or hydrocarbon in the state prior to the precursor.
  • the temperature of the fuel and its surrounding gas at which the growth process of hydrocarbon stops or ends in the state of a precursor of soot cannot be determined as a specific level since its depends upon the type of the fuel, air-fuel ratio, compression ratio and other factors. Nevertheless, the above certain temperature has a close relationship with the amount of NOx generated, and can be therefore defined by some degree based on the amount of NOx generated. Namely, as the EGR rate increases, the temperature of the fuel and its surrounding gas is lowered, and the amount of NOx generated is reduced. Almost no soot is produced when the amount of NOx generated is reduced to about 10 p.p.m. or smaller. Accordingly, the above-indicated certain temperature is substantially equal to the temperature at which the amount of NOx generated is about 10 p.p.m. or smaller.
  • soot is produced, it is impossible to purify the soot through an after treatment using a catalyst having an oxidizing function.
  • a precursor of soot or hydrocarbon in the state prior to that can be easily purified through an after treatment using a catalyst having an oxidizing function.
  • a considerably large difference arises as to whether hydrocarbon is discharged from the combustion chamber 5 in the form of a precursor of soot or its previous state, or in the form of soot.
  • the novel combustion system used in the present invention is characterized by discharging hydrocarbon in the form of a precursor of soot or its previous state from the combustion chamber 5 without producing soot in the combustion chamber 5, and oxidizing the thus discharged hydrocarbon by means of a catalyst having an oxidizing function.
  • the temperature of the fuel and its surrounding gas during combustion in the combustion chamber needs to be controlled to be lower than the temperature level at which soot is normally formed.
  • the temperature of the fuel and its surrounding gas, which is to be reduced is greatly influenced by the heat absorbing function of gas surrounding the fuel upon its combustion.
  • the fuel that has evaporated immediately reacts with oxygen in the air and burns.
  • the temperature of the air away from the fuel is not elevated so much, and only the temperature around the fuel is locally elevated to a considerably high level.
  • the air present away from the fuel hardly functions to absorb combustion heat of the fuel.
  • the combustion temperature is locally raised to an extremely high level, and therefore unburned hydrocarbon is exposed to the combustion heat, thereby to form soot.
  • the fuel exists in a mixture of a large amount of inert gas and a small amount of the air
  • evaporative fuel diffuses around, and reacts with oxygen that is mixed with the inert gas, and burns.
  • the combustion heat is absorbed by the surrounding inert gas, and therefore the combustion temperature does not rise so much, namely, the combustion temperature may be limited to a relatively low level.
  • the inert gas present in the combustion chamber plays an important role in lowering the combustion temperature, and thus the combustion temperature can be controlled to a relatively low level, utilizing the heat absorbing function of the inert gas.
  • inert gas it is necessary to provide inert gas in an amount large enough to absorb a sufficient quantity of heat so as to control the temperature of the fuel and its surrounding gas to be lower than the level at which soot is normally formed.
  • a required amount of inert gas increases with an increase in the amount of the fuel used for combustion.
  • the inert gas performs a more powerful or effective heat absorbing function as the specific heat of the inert gas is larger, and it is therefore preferable to use a gas having a larger specific heat as inert gas. Since CO 2 and EGR gas have a relatively large specific heat, it is desirable to use EGR gas as the inert gas.
  • Fig. 5 shows the relationship between the EGR rate and smoke when the EGR gas is used as inert gas and the EGR gas is cooled by varying degrees.
  • curve A represents the case where the EGR gas is powerfully cooled, and the temperature of the EGR gas is maintained at about 90 °C
  • curve B represents the case where the EGR gas is cooled by a small-sized cooling system
  • curve C represents the case where the EGR gas is not forcibly cooled.
  • the amount of soot generated reaches a peak at a point where the EGR rate is a little larger than 50%. In this case, almost no soot is produced if the EGR rate is controlled to be approximately 65% or greater.
  • the amount of soot generated reaches a peak at a point where the EGR rate is in the vicinity of 55%. In this case, almost no soot is produced if the EGR rate is controlled to be approximately 70% or greater.
  • Fig. 5 shows the amount of smoke generated by the engine when the engine load is relatively high.
  • the EGR rate at which the amount of soot generated reaches a peak is slightly reduced, and the lower limit of the EGR rate at which almost no soot is produced is also slightly lowered.
  • the lower limit of the EGR rate at which almost no soot is produced varies depending upon the degree of cooling of the EGR gas and the engine load.
  • Fig. 6 shows the amount of a mixed gas of EGR gas used as inert gas and the air, which is required for reducing the temperature of the fuel and its surrounding gas upon combustion to be lower than the level at which soot is produced, the proportion of the air in the mixed gas, and the proportion of the EGR gas in the mixed gas.
  • the vertical axis indicates the overall amount of gas that is introduced into the combustion chamber 5
  • one-dot chain line indicates the overall amount of gas that is introduced into the combustion chamber when the engine is not supercharged.
  • the horizontal axis indicates the required load
  • Z1 indicates a low-load engine operating region.
  • the proportion of the air namely, the amount of the air contained in the mixed gas
  • the proportion of the air represents such an amount of the air that is required for completely burning the fuel injected into the combustion chamber. Namely, in the case shown in Fig. 6, the ratio of the amount of the air to that of the fuel injected is equal to the stoichiometric air-fuel ratio.
  • the proportion of the EGR gas in Fig. 6, namely, the amount of the EGR gas contained in the mixed gas represents the minimum amount of EGR gas that is at least required for making the temperature of the fuel and its surrounding gas lower than the temperature level at which soot is formed.
  • This amount of EGR gas, as represented by EGR rate is approximately 55% or greater, and it is 70% or greater in the example of Fig. 6.
  • the amount of the EGR gas must be increased as the amount of fuel injected increases, as shown in Fig. 6. Namely, the amount of the EGR gas needs to be increased as the required load is increased.
  • the overall amount of intake gas X that is required for preventing generation of soot exceeds the overall amount of the intake gas Y that can be sucked or introduced into the combustion chamber. In this case, therefore, both the EGR gas and the intake air or only the EGR gas needs to be supercharged or pressurized so that the overall amount of intake gas X required for inhibiting generation of soot is supplied into the combustion chamber 5.
  • the overall amount of intake gas X coincides with the overall amount of intake gas that can be introduced into the combustion chamber. To prevent generation of soot in this case, therefore, the amount of the air is slightly reduced, and the amount of the EGR gas is increased, so that the fuel is burned with the air-fuel ratio being controlled to be rich.
  • Fig. 6 shows the case where the fuel is burned at the stoichiometric air-fuel ratio.
  • the amount of NOx generated can be controlled to around 10 p.p.m. or less while preventing generation of soot, even if the amount of the air is smaller than that as indicated in Fig. 6, and the air-fuel ratio is rich.
  • the amount of NOx generated can be controlled to around 10 p.p.m. or less while preventing generation of soot.
  • the combustion temperature is controlled to a low level, and therefore no soot is produced at all. Furthermore, only a slight amount of NOx is generated.
  • the temperature of the fuel and its surrounding gas upon combustion thereof in the combustion chamber is controlled to be equal to or lower than the level at which the growth of hydrocarbon is stopped midway, only when the engine load is relatively low, and a small quantity of heat is generated by the combustion.
  • the first mode of combustion, or low-temperature combustion is carried out such that the temperature of the fuel and its surrounding gas upon combustion is controlled to be equal to or lower than the temperature level at which the growth of hydrocarbon is stopped midway.
  • the second mode of combustion or conventional combustion that has been ordinarily performed, is carried out.
  • the amount of inert gas within the combustion chamber is larger than that at which the amount of soot generated reaches a peak, as is apparent from the above explanation.
  • the amount of inert gas within the combustion chamber is smaller than that at which the amount of soot generated reaches a peak.
  • Fig. 7 shows the first operating region I in which the first mode of combustion, or low-temperature combustion, is conducted, and the second operating region II in which the second mode of combustion, or conventional combustion, is conducted.
  • the vertical axis L indicates the amount of depression of the accelerator pedal 40, namely, the required load
  • the horizontal axis N indicates the engine speed.
  • X(N) represents the first boundary between the first operating region I and the second operating region II
  • Y(N) represents the second boundary between the first operating region I and the second operating region II.
  • a shift from the first operating region I to the second operating region II is judged based on the first boundary X(N), and a shift from the second operating region II to the first operating region I is judged based on the second boundary Y(N).
  • the engine is judged as shifting from the first operating region I to the second operating region II, and combustion is performed in the conventional combustion method. If the required load L is subsequently reduced to be lower than the second boundary Y(N) as a function of the engine speed N, the engine is judged as shifting from the second operating region II to the first operating region I, and low-temperature combustion is performed again.
  • Fig. 8 shows the output of the air-fuel ratio sensor 21.
  • the output current I of the air-fuel ratio sensor 21 varies in accordance with the air-fuel ratio A/F. Accordingly, the air-fuel ratio can be determined from the output current I of the air-fuel ratio sensor 21.
  • Fig. 9 shows the opening of the throttle valve 16 against the required load L, the opening of the EGR control valve 23, the EGR rate, the air-fuel ratio, the injection timing, and the amount of fuel injected.
  • the opening of the throttle valve 16 gradually increases from the vicinity of the fully closed position to about a half-open position as the required load L increases, and the opening of the EGR control valve 23 increases from the vicinity of the fully closed position to the full-open position as the required load L increases, as shown in Fig. 9.
  • the EGR rate is controlled to about 70%, and the air-fuel ratio is made slightly lean.
  • the opening of the throttle valve 16 and the opening of the EGR control valve 23 are controlled in the first operating region I so that the EGR rate is approximated to 70%, and the air-fuel ratio is made slightly lean.
  • the air-fuel ratio is controlled to a target lean air-fuel ratio based on the output signal of the air-fuel ratio sensor 21 by correcting or adjusting the opening of the EGR control valve 23.
  • the fuel is injected into the combustion chamber before the piston reaches the compression top dead center TDC.
  • the injection start timing ⁇ S is delayed as the required load L increases, and the injection completion timing ⁇ E is also delayed with a delay in the injection start timing ⁇ S.
  • the throttle valve 16 is placed in the vicinity of the fully closed position, and the EGR control valve 23 is also placed in the vicinity of the fully closed position.
  • the throttle valve 16 With the throttle valve 16 almost fully closed, the pressure within the combustion chamber 5 at the beginning of compression is reduced, and therefore the compression pressure is reduced.
  • the compression pressure is reduced, compression work done by the piston 4 is reduced with a result of reduction in vibration of the engine main body 1.
  • the throttle valve 16 is placed in the vicinity of the fully closed position during idling of the engine so as to suppress vibration of the engine main body 1.
  • the engine performs conventional combustion in the second operating region II. Although some soot and NOx are produced in this combustion mode, the engine exhibits an improved thermal efficiency as compared with that in the case of low-temperature combustion, and therefore the amount of fuel injected steps down as shown in Fig. 9 when the engine operating region changes from the first operating region I to the second operating region II.
  • the throttle valves 16 of the engine except a part thereof are kept in the full-open state, and the opening of the EGR control valve 23 is gradually reduced as the required load L increases.
  • the EGR rate decreases with an increase in the required load L
  • the air-fuel ratio decreases with an increase in the required load L. It is, however, to be noted that the air-fuel ratio is kept in the lean range even if the required load L is increased.
  • the injection start timing ⁇ S is in the vicinity of the compression top dead center TDC.
  • Fig. 10 shows the air-fuel ratio A/F in the first operating region I.
  • the air-fuel ratio is lean in the first operating region I, and the air-fuel ratio A/F is increased to be even leaner as the required load L is reduced in the first operating region I.
  • the quantity of heat generated upon combustion is reduced as the required load L is reduced.
  • the air-fuel ratio increases with a reduction in the EGR rate, and therefore the air-fuel ratio A/F is increased with a reduction in the required load L as shown in Fig. 10.
  • the fuel consumption rate is improved as the air-fuel ratio is increased. In the present embodiment, therefore, the air-fuel ratio A/F is increased to be as lean as possible as the required load L is reduced.
  • the fuel injection amount Q in the first operating region I is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N.
  • the target opening ST of the throttle valve 16 that is required to make the air-fuel ratio equal to the target air-fuel ratio as indicated in Fig. 10 is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N, as shown in Fig. 12A.
  • the target opening SE of the EGR control valve 23 required to make the air-fuel ratio equal to the target air-fuel ratio as indicated in Fig. 10 is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N, as shown in Fig. 12B.
  • Fig. 13 shows the target air-fuel ratio when the second mode of combustion, or ordinary combustion by the conventional combustion method, is performed.
  • the fuel injection amount Q in the second operating region II is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N.
  • the target opening ST of the throttle valve 16 that is required to make the air-fuel ratio equal to the target air-fuel ratio as shown in Fig. 13 is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N, as shown in Fig. 15A.
  • the target opening SE of the EGR control valve 23 required to make the air-fuel ratio equal to the target air-fuel ratio as shown in Fig. 13 is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N.
  • the particulate filter 19 carries thereon an NOx absorbent.
  • the NOx absorbent includes alumina, for example, as a carrier, and at least one selected from, for example, alkali metals, such as potassium K, sodium Na, lithium Li and cesium CS, alkali earth metals, such as barium Ba and calcium Ca, and rare earth metals, such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt are carried on the carrier.
  • alkali metals such as potassium K, sodium Na, lithium Li and cesium CS
  • alkali earth metals such as barium Ba and calcium Ca
  • rare earth metals such as lanthanum La and yttrium Y
  • a noble metal such as platinum Pt
  • the NOx absorbent performs NOx absorbing and releasing functions, namely, is adapted to absorb NOx when the air-fuel ratio of exhaust gas is lean, and release the thus absorbed NOx when the air-fuel ratio of exhaust gas is equal to the stoichiometric air-fuel ratio or rich.
  • NOx absorbent actually performs NOx absorbing and releasing functions if the particulate filter 19 carrying the NOx absorbent is disposed in the engine exhaust passage, detailed mechanisms of these NOx absorbing and releasing functions have not been clarified. It is, however, considered that the NOx absorbing and releasing functions be performed according to a mechanism as shown in Fig. 16. While this mechanism will be hereinafter explained with respect to the case where platinum Pt and barium Ba are carried by the carrier, a similar mechanism equally applies where other noble metal, alkali metal, alkali earth metal, and/or rare earth metal is/are used.
  • combustion generally takes place in the combustion chamber 5 in the conthtion that the air-fuel ratio is in a lean range.
  • a high concentration of oxygen is contained in the exhaust gas, and oxygen O 2 is deposited in the form of O 2 - or O 2- on the surface of platinum Pt as shown in Fig. 16A.
  • NO contained in the flowing exhaust gas reacts with O 2 - or O 2- on the surface of platinum Pt, to form NO 2 (2NO + O 2 ⁇ 2NO 2 ).
  • NO 2 is formed on the surface of platinum Pt as long as the exhaust gas contains a high concentration of oxygen, and NO 2 is absorbed into the absorbent to form nitrate ion NO 3 - as long as the NOx absorbing capability of the absorbent is not saturated.
  • NOx released from the NOx absorbent reacts with unburned HC and CO contained in exhaust gas, and is eventually reduced, as shown in Fig. 16B. If no NO 2 is present on the surface of platinum Pt, NO 2 is successively released from the absorbent. Thus, NOx is released from the NOx absorbent in a short time once the air-fuel ratio of the flowing exhaust gas turns rich, and the released NOx is reduced, thus preventing NOx from being discharged or released to the atmosphere.
  • NOx is released from the NOx absorbent even if the air-fuel ratio of the flowing exhaust gas is substantially equal to the stoichiometric air-fuel ratio.
  • the air-fuel ratio of the flowing exhaust gas is controlled to the stoichiometric air-fuel ratio, however, NOx is only slowly released from the NOx absorbent, and therefore it takes a relatively long time to release the whole NOx absorbed in the NOx absorbent.
  • the amount of NOx absorbed "A" per unit time during the first mode of combustion is obtained in advance according to a map as shown in Fig. 17A as a function of the required load L and the engine speed N
  • the amount of NOx absorbed "B" per unit time during the second mode of combustion is obtained in advance according to a map as shown in Fig. 17B as a function of the required load L and the engine speed N.
  • the amount of NOx released "C" per unit time when the air-fuel ratio turns rich or becomes equal to the stoichiometric ratio during the first mode of combustion is obtained in advance according to a map as shown in Fig. 17C as a function of the air-fuel ratio A/F and the amount of the intake air QA.
  • the total amount of NOx absorbed in the NOx absorbent ⁇ NOX is then estimated by integrating or summing up the NOx absorption amounts "A" and "B" per unit time, and subtracting the NOx release amount "C” per unit time from the sum.
  • the amount of intake air is calculated based on the required load L and the engine speed N.
  • NOx is released from the NOx absorbent when the total NOx absorption amount ⁇ NOX exceeds a predetermined permissible maximum value MAX.
  • the air-fuel ratio in the combustion chamber 5 is temporarily controlled to be rich so that NOx can be released from the NOx absorbent. As described above, substantially no soot is produced even if the air-fuel ratio turns rich during low-temperature combustion.
  • additional fuel is injected into the combustion chamber in the latter half of an expansion stroke or during an exhaust stroke.
  • the amount of the additional fuel is determined so that the air-fuel ratio of exhaust gas flowing into the NOx absorbent becomes rich. With the additional fuel thus injected, NOx is released from the NOx absorbent.
  • Fig. 18 shows a control routine for setting an NOx release flag that is to be set when NOx should be released from the NOx absorbent. This routine is executed by interrupting a main control routine at certain time intervals.
  • step 100 is initially executed to determine whether a flag I indicating that the current engine operating region is the first operating region I is set or not. If the flag I is set, namely, if the engine is operating in the first operating region I, the control flow goes to step 101 to calculate the amount "A" of NOx absorbed per unit time, based on the map as shown in Fig. 17A. Step 102 is then executed to calculate the amount "C" of NOx released per unit time, based on the map as shown in Fig. 17C. In the next step 103, "A" is added to the total NOx absorption amount ⁇ NOX, and “C” is subtracted from the total NOx absorption amount ⁇ NOX. Step 104 is then executed to determine whether the total NOx absorption amount ⁇ NOX exceeds the permissible maximum value MAX. If ⁇ NOX is larger than MAX, the control flow goes to step 105 to set the NOx release flag.
  • step 100 determines that the flag I is reset, namely, the current engine operating region is the second operating region II
  • the control flow goes to step 106 to calculate the amount "B" of NOx absorbed per unit time, based on the map as shown in Fig. 17B.
  • step 107 "B" is added to the total NOx absorption amount ⁇ NOX.
  • Step 108 is then executed to determine whether the total NOx absorption amount ⁇ NOX exceeds the permissible maximum value MAX. If ⁇ NOX is larger than MAX, the control flow goes to step 109 to set the NOx release flag.
  • SOx is also contained in exhaust gas, and the NOx absorbent absorbs SOx as well as NOx.
  • the mechanism by which SOx is absorbed by the NOx absorbent is considered to be substantially the same as the NOx absorption mechanism as described above.
  • part of SO 3 thus formed is absorbed into the absorbent while being further oxidized on platinum Pt, and diffuses within the absorbent in the form of sulfate ion SO 4 2- while combining with barium oxide BaO, to thus form stable sulfate BaSO 4 .
  • the sulfate BaSO 4 thus formed is stable and hard to decompose, and is therefore likely to remain as it is without being decomposed even if the air-fuel ratio of exhaust gas is simply made rich. Accordingly, the amount of sulfate BaSO 4 in the NOx absorbent increases with time, and the amount of NOx that can be absorbed by the NOx absorbent is reduced with time. If the temperature of the NOx absorbent becomes equal to or higher than a certain temperature, e.g., 600 °C, the sulfate BaSO 4 decomposes within the NOx absorbent, and SOx is released from the NOx absorbent if the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is controlled to be rich.
  • a certain temperature e.g. 600 °C
  • the temperature of the NOx absorbent is maintained at a high level during the first mode of combustion, and the air-fuel ratio of the exhaust gas is controlled to be rich, so that SOx is released from the NOx absorbent.
  • Fig. 19 is a control routine for setting an SOx release flag when SOx should be released from the NOx absorbent.
  • step 120 is initially executed to calculate an integrated value ⁇ Q of the fuel injection amount by adding an amount "Q" of fuel injected to ⁇ Q.
  • Step 121 is then executed to determine whether the integrated value ⁇ Q of the fuel injection amount has exceeded the permissible maximum value Q0. If ⁇ Q becomes larger than Q0, the control flow goes to step 122 to set the SOx release flag, and then goes to step 123 to make ⁇ Q equal to zero. Since a certain amount of sulfur is contained in the fuel, the integrated value ⁇ Q of the fuel injection amount is proportional to the amount of SOx absorbed by the NOx absorbent. When ⁇ Q becomes greater than Q0, therefore, the SOx release flag is set.
  • a noble metal such as platinum
  • the NOx absorbent has an oxidizing function
  • the unburned hydrocarbon discharged from the combustion chamber 5 can be favorably oxidized by the NOx absorbent.
  • particulates consisting of soot or soluble substances SOF are discharged from the combustion chamber, and successively deposited on the particulate filter 19. Accordingly, the amount of particulates deposited on the particulate filter 19 gradually increases with time.
  • the particulates are caused to burn when the amount of the particulates deposited on the particulate filter 19 exceeds its permissible amount.
  • the temperature at which the particulates are favorably burned is in a range of about 500 °C to 600 °C. When the particulates are to be burned, therefore, the temperature of the particulate filter 19 is raised to 500°C ⁇ 600°C, and maintained at 500°C ⁇ 600°C until the combustion of all of the particulates is completed.
  • Fig. 20 is a control routine for setting a PM (Particulate Matter) combustion flag when the particulates are to be burned.
  • step 140 is initially executed to determine whether a difference ⁇ P between the pressure on the upstream side of the particulate filter 19 and that on the downstream side of the filter 19 has exceeded a permissible value P1 or not. If ⁇ P becomes larger than P1, the control flow goes to step 141 to set the PM combustion flag.
  • Fig. 21 shows the case where the PM combustion flag is set in an attempt to burn particulates when the first mode of combustion (low-temperature combustion) takes place with the current average air-fuel ratio in the combustion chamber 5 being in a lean range.
  • the initial temperature raising control as shown in Fig. 21 is performed.
  • the average air-fuel ratio in the combustion chamber 5 is controlled to be richer than said current average air-fuel ratio, preferably to be stoichiometric or rich, during the initial temperature raising control.
  • the initial temperature raising control is performed until the temperature of the particulate filter 19 detected by the temperature sensor 29 reaches the upper-limit temperature MAX suitable for combustion of the particulates.
  • Fig. 21 also shows the lower-limit temperature MIN that is required to favorably continue combustion of the particulates.
  • part of the air in the combustion chamber 5 is not used for combustion even if the average air-fuel ratio in the combustion chamber 5 is rich, and therefore a large amount of remaining oxygen and a large amount of unburned HC are discharged from the combustion chamber 5. At this time, however, almost no soot is generated, as described above. If a large amount of remaining oxygen and a large amount of unburned HC are discharged from the combustion chamber 5 in this manner, the unburned HC is oxidized in a moment on the particulate filter 19. As a result, a large quantity of heat due to the oxidizing reaction is generated, and therefore the temperature TC of the particulate filter 19 is elevated.
  • the temperature TC of the particulate filter 19 can also be relatively rapidly raised even where the average air-fuel ratio in the combustion chamber 5 is equal to the stoichiometric air-fuel ratio. In this case, however, the amount of unburned HC discharged from the combustion chamber 5 is smaller than that in the case where the average air-fuel ratio is rich, and therefore the temperature TC of the particulate filter 18 cannot be raised as rapidly as in the case where the average air-fuel ratio is rich. Where the average air-fuel ratio in the combustion chamber 5 is lean, the amount of unburned HC discharged from the combustion chamber 5 is small, and therefore the temperature of the particulate filter 19 cannot be expected to increase rapidly in this case.
  • a stratified charge combustion type internal combustion engine wherein an air-fuel mixture is formed in a limited region within the combustion chamber, and the air-fuel mixture is fired by a spark plug, a larger amount of remaining oxygen and a large amount of unburned HC are discharged from the combustion chamber if the average air-fuel ratio in the combustion chamber is rich.
  • the present invention may be equally applied to such a stratified charge combustion type engine.
  • particulates on the particulate filter 19 start burning.
  • temperature maintaining control is performed in which the temperature TC of the particulate filter 19 is maintained at a level equal to or higher than the lower-limit temperature MIN so that the particulates are continuously burned.
  • the first mode of combustion is performed while the average air-fuel ratio in the combustion chamber 5 is controlled to be lean under the temperature maintaining control, as shown in Fig. 21.
  • the average air-fuel ratio may also be maintained at the stoichiometric air-fuel ratio.
  • intermediate temperature raising control is performed.
  • the average air-fuel ratio in the combustion chamber 5 is controlled to be richer than said current average air-fuel ratio, preferably stoichiometric or rich, in the first combustion mode, as shown in Fig. 21. If the average air-fuel ratio in the combustion chamber 5 turns richer than said current average air-fuel ratio, preferably stoichiometric or rich, the temperature TC of the particulate filter 19 is raised.
  • NOx release control is performed, and the average air-fuel ratio in the combustion chamber 5 is controlled to be rich in the first combustion mode, as shown in Fig. 21.
  • NOx is released from the NOx absorbent.
  • the temperature TC of the particulate filter 19 is raised.
  • Fig. 22 shows the case where the PM combustion flag is set in an attempt to burn particulates during the second mode of combustion while the average air-fuel ratio in the combustion chamber 5 is lean.
  • the initial temperature raising control is performed as shown in Fig. 22.
  • the initial temperature raising control during the second mode of combustion is roughly classified into two methods. One of these methods is to increase the amount of unburned HC discharged, and the other method is to increase the temperature of exhaust gas.
  • the first method of increasing the amount of unburned HC discharged may be practiced in two manners.
  • the fuel injection timing is changed so as to increase the amount of unburned HC generated in the combustion chamber 5.
  • additional fuel is injected into the combustion chamber 5 after injection of main fuel, and then discharged from the combustion chamber 5 without being completely burned.
  • the second method of increasing the temperature of exhaust gas may be practiced by delaying the fuel injection timing.
  • a method of increasing the temperature of exhaust gas by a large degree a small amount of auxiliary fuel is injected before injection of main fuel, and the injection timing of the main fuel is further delayed.
  • misfiring may occur if the injection is too late.
  • the injection timing can be delayed without causing misfiring of the engine if a small amount of auxiliary fuel is injected, and consequently the temperature of the exhaust gas can be significantly increased.
  • the initial temperature raising control may be performed in any of the methods as described above. As one example, there will be described the case where the injection timing is delayed upon the initial temperature raising control.
  • the temperature TC of the particulate filter 19 is raised as shown in Fig. 22, and combustion of particulates on the particulate filter 19 is started. If the temperature TC of the particulate filter 19 is subsequently reduced down to the lower-limit temperature MIN, the primary temperature raising control is performed. Under the primary temperature raising control, the fuel injection timing is further delayed so that the temperature of exhaust gas is increased. If the temperature TC of the particulate filter 19 is reduced down to the lower-limit temperature MIN again, the secondary temperature raising control is performed. Under the secondary temperature raising control, auxiliary fuel is injected before injection of main fuel, and at the same time the injection timing of the main fuel is further delayed, so that the temperature of exhaust gas is increased.
  • NOx release control is performed when the NOx release flag is set, and an additional fuel is injected during an expansion stroke or exhaust stroke of the engine after the injection of main fuel so that the average air-fuel ratio in the combustion chamber 5 becomes rich, as shown in Fig. 22.
  • NOx is released from the NOx absorbent.
  • the temperature TC of the particulate filter 19 is elevated.
  • Fig. 23 shows a SOx release process.
  • the SOx release flag when the SOx release flag is set, the average air-fuel ratio in the combustion chamber 5 is maintained in a rich range in the first combustion mode as shown in Fig. 23 until release of SOx is completed.
  • Fig. 24A and Fig. 24B show the case where it was determined that combustion of particulates, or PM combustion process, and SOx release process should be both conducted at the same time. More specifically, where the amount of SOx absorbed in the NOx absorbent is larger than a predetermined value when the PM combustion flag is set, or where the amount of particulates deposited onto the particulate filter 19 is larger than a predetermined value when the SOx release flag is set, it is determined that the PM combustion process and the SOx release process should be both carried out at the same time. In this case, the SOx release process may be executed immediately after completion of the PM combustion process, as shown in Fig. 24A, or the PM combustion process may be executed immediately after completion of the SOx release process, as shown in Fig. 24B.
  • step 200 is initially executed to determine whether the flag I is set or not, namely, whether the engine is currently in the first operating region I. If the flag I is set, namely, if the engine is in the first operating region I, the control flow goes to step 201 to determine whether the required load L becomes larger than the first boundary X1(N). If L is equal to or smaller than X1, the control flow goes to step 203 in which low-temperature combustion is performed.
  • a target opening ST of the throttle valve 16 is obtained from the map as shown in Fig. 12A, and the opening of the throttle valve 16 is controlled to the target opening ST.
  • a target opening SE of the EGR control valve 23 is obtained from the map as shown in Fig. 12B, and the opening of the EGR control valve 23 is controlled to the target opening SE.
  • Step 205 is then executed to determine whether either the PM combustion flag or the SOx release flag is set or not. If neither the PM combustion flag nor the SOx release flag is set, the control flow goes to step 206.
  • step 206 it is determined whether the NOx release flag is set or not. If the NOx release flag is not set, the control flow goes to step 207 to perform fuel injection based on the map as shown in Fig. 11 so as to provide the air-fuel ratio as indicated in Fig. 10. At this time, low-temperature combustion is performed with a lean air-fuel ratio. If step 206 determines that the NOx release flag is set, the control flow goes to step 208 in which fuel injection control is performed so that the average air-fuel ratio in the combustion chamber 5 becomes rich. As a result, NOx is released from the NOx absorbent. Step 209 is then executed to reset the NOx release flag.
  • step 205 determines that either the PM combustion flag or the SOx release flag is set
  • the control flow goes to step 210 to determine whether both of the PM combustion process and SOx release process should be executed at the same time. If step 210 determines that the PM combustion process and the SOx release process need not be both executed at the same time, the control flow goes to step 211 to determine whether the PM combustion flag is set or not.
  • step 212 the control flow goes to step 212 to carry out the PM combustion process I as shown in Fig. 21.
  • a routine for implementing the PM combustion process I is illustrated in Fig. 27. If the PM combustion flag is not set, namely, when the SOx release flag is set, on the other hand, the control flow goes to step 213 to carry out the SOx release process as shown in Fig. 23.
  • a routine for implementing the SOx release process is illustrated in Fig. 29.
  • step 210 determines that the PM combustion process and the SOx release process should be both executed at the same time, on the other hand, the control flow goes to step 214 to carry out the PM combustion and SOx release process as shown in Fig. 24A or Fig. 24B.
  • a routine for implementing the PM combustion and SOx release process shown in Fig. 24 A is illustrated in Fig. 30 and Fig. 31, and a routine for implementing the PM combustion and SOx release process shown in Fig. 24B is illustrated in Fig. 32 and Fig. 33.
  • step 201 determines that L is larger than X(N)
  • the control flow goes to step 202 to reset the flag I
  • step 217 a target opening ST of the throttle valve 16 is obtained from the map as shown in Fig. 15A, and the opening of the throttle valve 16 is controlled to the target opening ST.
  • a target opening SE of the EGR control valve 23 is obtained from the map as shown in Fig. 15B, and the opening of the EGR control valve 23 is controlled to the target opening SE.
  • Step 219 is then executed to determine whether the PM combustion flag is set or not.
  • the control flow goes to step 220 to determine whether the NOx release flag is set or not. If the NOx release flag is not set, the control flow goes to step 221 in which fuel injection is performed based on the map as shown in Fig. 14 so as to provide the air-fuel ratio as indicated in Fig. 13. At this time, the second mode of combustion is performed with a lean air-fuel ratio. If step 220 determines that the NOx release flag is set, on the other hand, the control flow goes to step 222 in which additional fuel is injected into the combustion chamber so that the air-fuel ratio of exhaust gas flowing into the NOx absorbent turns rich.
  • step 219 determines that the PM combustion flag is set, on the other hand, the control flow goes to step 224 to execute the PM combustion process II as shown in Fig. 22.
  • a routine for implementing the PM combustion process II is illustrated in Fig. 28.
  • step 200 determines whether the required load L gets smaller than the second boundary Y(N). If L is equal to or greater than Y(N), the control flow goes to step 217 to perform the second mode of combustion. If step 215 determines that the required load L is smaller than the second boundary Y(N), on the other hand, the control flow goes to step 216 to set the flag I. The control flow then proceeds to step 203 to perform low-temperature combustion.
  • step 300 is initially executed to determine whether the initial temperature raising control has been completed or not. If the initial temperature raising control has not been completed, the control flow goes to step 301 to perform the initial temperature raising control, and then goes to step 308. If step 300 determines that the initial temperature raising control has been completed, step 302 is then executed to determine whether the temperature TC of the particulate filter 19 is lower than the lower-limit temperature MIN. If TC is equal to or higher than MIN, the control flow goes to step 303 to perform temperature maintaining control, and then goes to step 305. If step 303 determines that TC is lower than MIN, on the other hand, the control flow goes to step 304 to start intermediate temperature control. Once TC falls below MIN, the intermediate temperature control is kept performed until the temperature TC of the particulate filter 19 reaches the upper-limit temperature MAX.
  • step 305 it is determined whether the NOx release flag is set or not. If the NOx release flag is not set, the control flow goes to step 308 skipping steps 306 and 307. If step 305 determines that the NOx release flag is set, on the other hand, the control flow goes to step 306 to control the fuel injection amount so that the air-fuel ratio becomes rich, and then goes to step 307 to reset the NOx release flag. Step 308 is then executed to determine whether a difference ⁇ P in the pressure detected by the differential pressure sensor 20 becomes smaller than a predetermined value P2, and if an affirmative decision (YES) is obtained in step 308, namely, if ⁇ P ⁇ P2, the control flow goes to step 309 to reset the PM combustion flag.
  • YES affirmative decision
  • step 400 is initially executed to determine whether a certain period of time has elapsed since the PM combustion flag is set. If the above certain time has not elapsed, the control flow goes to step 401 to zero the value C that represents the state of the temperature raising control. Step 405 is then executed to determine whether C is zero or not, and, when C is equal to 0, the control flow goes to step 407 to perform the initial temperature raising control. The control flow then proceeds to step 410. If step 400 determines that a definite period of time has elapsed since the PM combustion flag is set, the control flow goes to step 402 to determine whether it is currently within a wait time that starts upon switching from the initial temperature raising control to the primary temperature raising control. The control flow goes to step 403 when the initial temperature raising control is performed.
  • step 403 it is determined whether the temperature TC of the particulate filter 19 falls below the lower-limit temperature MIN or not. If TC is equal to or higher than MIN, the control flow goes to step 405, and then goes to step 407 to continue the initial temperature raising control. If step 403 determines that TC is lower than MIN, on the other hand, the control flow goes to step 404 to increment C by 1. After execution of step 405, step 406 is executed to determine whether C is equal to 1 or not. Since C is equal to 1 in the current control cycle, the control flow goes to step 408 to perform the primary temperature raising control, and then goes to step 410. For a definite period of time that starts upon switching from the initial temperature raising control to the primary temperature raising control, it is determined to be within the waiting time, and therefore the control flow goes from step 402 to steps 405, 406, 408, to keep performing the primary temperature raising control.
  • step 403 determines that TC is lower than MIN
  • step 404 makes C equal to 2.
  • step 406 goes from step 406 to step 409 to perform the secondary temperature raising control.
  • step 410 it is determined whether the NOx release flag is set or not. When the NOx release flag is not set, the control flow jumps to step 413. If step 410 determines that the NOx release flag is set, the control flow goes to step 411 to control the amount of fuel injected so as to make the air-fuel ratio rich, and the NOx release flag is reset in step 412. Step 413 is then executed to determine whether a difference ⁇ P in the pressure detected by the differential pressure sensor 20 is smaller than a predetermined value P2, and when ⁇ P is smaller than the predetermined value P2, the control flow goes to step 414 to reset the PM combustion flag.
  • step 500 is initially executed to control the fuel injection amount so that the average air-fuel ratio in the combustion chamber 5 becomes rich.
  • Step 501 is then executed to reset the NOx release flag.
  • Step 502 is then executed to determine whether the operation to release SOx absorbed in the NOx absorbent has been completed or not. If the SOx releasing operation is completed, the control flow goes to step 503 to reset the SOx release flag.
  • step 600 is initially executed to determine whether PM combustion process has been completed or not.
  • the control flow goes to step 601 to determine whether the initial temperature raising control has been completed.
  • the control flow goes to step 602 to perform the initial temperature raising control, and the control flow then goes to step 609.
  • step 601 determines that the initial temperature raising control has been completed
  • the control flow goes to step 603 to determine whether the temperature TC of the particulate filter 19 falls below the lower-limit temperature MIN.
  • TC is equal to or higher than MIN
  • the control flow goes to step 604 to perform temperature maintaining control, and then goes to step 606.
  • step 603 determines that TC is lower than MIN
  • the control flow goes to step 605 to start intermediate temperature control. Once TC falls below MIN, the intermediate temperature control is kept performed until the temperature TC of the particulate filter 18 reaches the upper-limit temperature MAX.
  • step 606 it is determined whether the NOx release flag is set or not. If NOx release flag is not set, the control flow goes to step 609 skipping steps 607 and 608. If step 606 determines that the NOx release flag is set, the control flow goes to step 607 to control the fuel injection amount so that the air-fuel ratio becomes rich, and then goes to step 608 to reset the NOx release flag. In step 609, it is determined whether a difference ⁇ P in the pressure detected by the differential pressure sensor 20 is equal to or smaller than a predetermined value P2. If ⁇ P is smaller than P2, the control flow goes to step 610 to reset the PM combustion flag.
  • step 600 determines that the PM combustion process has been completed, the control flow goes to step 611 to control the fuel injection amount so that the average air-fuel ratio in the combustion chamber 5 becomes rich. Step 612 is then executed to reset the NOx release flag. In the next step 613, it is determined whether the operation to release SOx absorbed in the NOx absorbent has been completed. If the SOx releasing operating has been completed, the control flow goes to step 614 to reset the SOx release flag.
  • step 700 is initially executed to determine whether the SOx release process has been completed or not. If the SOx release process has not been completed, the control flow goes to step 701 to control the amount of fuel injected so that the average air-fuel ratio in the combustion chamber 5 becomes rich. Step 703 is then executed to determine whether the operation to release SOx absorbed in the NOx absorbent has been completed or not. If the SOx releasing operation has been completed, the control flow goes to step 704 to reset the SOx release flag.
  • step 700 determines that the SOx release process has been completed, the control flow goes to step 705 to determine whether the temperature TC of the particulate filter 19 falls below the lower-limit temperature MIN. If TC is equal to or higher than MIN, the control flow goes to step 706 to perform temperature maintaining control, and then goes to step 708. If step 705 determines that TC is lower than MIN, on the other hand, the control flow goes to step 707 to start intermediate temperature control. Once TC falls below MIN, the intermediate temperature control is kept performed until the temperature TC of the particulate filter 19 reaches the upper-limit temperature MAX.
  • step 708 it is determined whether the NOx release flag is set or not. If the NOx release flag is not set, the control flow goes to step 711 skipping steps 709 and 710. If step 708 determines that the NOx release flag is set, the control flow goes to step 709 to control the fuel injection amount so as to make the air-fuel ratio rich. Step 710 is then executed to reset the NOx release flag. In the next step 711, it is determined whether a difference ⁇ P in the pressure detected by the differential pressure sensor 20 becomes smaller than a predetermined value P2 or not. If ⁇ P becomes smaller than P2, the control flow goes to step 712 to reset the PM combustion flag.
  • the temperature of the particulate trapping device can be rapidly raised to a level at which the particulates can be burned.
  • An internal combustion engine which is selectively operable in the first combustion mode in which the amount of EGR gas in the combustion chamber (5) is larger than that of the EGR gas with which the amount of soot generated reaches a peak, and the second combustion mode in which the amount of EGR gas in the combustion chamber (5) is smaller than that of the EGR gas with which the amount of soot generated reaches the peak.
  • a particulate trapping device (18) that carries an NOx absorbent is disposed in an exhaust passage of the engine. When the temperature of the particulate trapping device (18) should be increased to a temperature level at which particulates can be burned, the average air-fuel ratio in the combustion chamber (5) is temporarily controlled to be richer than the current average air-fuel ratio.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Exhaust-Gas Circulating Devices (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Processes For Solid Components From Exhaust (AREA)
  • Output Control And Ontrol Of Special Type Engine (AREA)
EP00117716A 1999-08-26 2000-08-17 Moteur à combustion interne Expired - Lifetime EP1079084B1 (fr)

Applications Claiming Priority (2)

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JP24022399A JP3304929B2 (ja) 1999-08-26 1999-08-26 内燃機関
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003037507A1 (fr) * 2001-10-27 2003-05-08 Johnson Matthey Public Limited Company Ligne d'echappement pour moteur a combustion interne
FR2892766A1 (fr) 2005-10-27 2007-05-04 Renault Sas Dispositif de traitement d'oxydes d'azote pour gaz d'echappement de vehicule automobile
US7219008B2 (en) * 2003-06-30 2007-05-15 Renault S.A.S. Method and device for estimating a nitrogen oxide mass stored in a catalytic trapping device of a motor vehicle
US7832203B2 (en) 2001-10-27 2010-11-16 Johnson Matthey Public Limited Company Exhaust system for a lean burn internal combustion engine

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JP3552674B2 (ja) * 2000-03-27 2004-08-11 トヨタ自動車株式会社 内燃機関の排気浄化装置
US7197867B2 (en) 2004-10-04 2007-04-03 Southwest Research Institute Method for the simultaneous desulfation of a lean NOx trap and regeneration of a Diesel particulate filter

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US4211075A (en) * 1978-10-19 1980-07-08 General Motors Corporation Diesel engine exhaust particulate filter with intake throttling incineration control
US5207058A (en) * 1990-11-16 1993-05-04 Toyota Jidosha Kabushiki Kaisha Internal combustion engine
US5771686A (en) * 1995-11-20 1998-06-30 Mercedes-Benz Ag Method and apparatus for operating a diesel engine
EP0903481A1 (fr) * 1997-03-31 1999-03-24 Mitsubishi Jidosha Kogyo Kabushiki Kaisha Dispositif de purification de gaz d'echappement d'un moteur a combustion interne, a injection et a cylindres
EP0879946A2 (fr) * 1997-05-21 1998-11-25 Toyota Jidosha Kabushiki Kaisha Moteur à combustion interne
EP0919708A2 (fr) * 1997-11-25 1999-06-02 Toyota Jidosha Kabushiki Kaisha Moteur à allumage par compression
EP0921285A2 (fr) * 1997-12-04 1999-06-09 Toyota Jidosha Kabushiki Kaisha Moteur diesel
WO1999032766A1 (fr) * 1997-12-22 1999-07-01 Ford Global Technologies, Inc. Regulation de la temperature des dispositifs antipollution couples aux moteurs a injection directe

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003037507A1 (fr) * 2001-10-27 2003-05-08 Johnson Matthey Public Limited Company Ligne d'echappement pour moteur a combustion interne
US7832203B2 (en) 2001-10-27 2010-11-16 Johnson Matthey Public Limited Company Exhaust system for a lean burn internal combustion engine
US7219008B2 (en) * 2003-06-30 2007-05-15 Renault S.A.S. Method and device for estimating a nitrogen oxide mass stored in a catalytic trapping device of a motor vehicle
FR2892766A1 (fr) 2005-10-27 2007-05-04 Renault Sas Dispositif de traitement d'oxydes d'azote pour gaz d'echappement de vehicule automobile

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JP3304929B2 (ja) 2002-07-22
EP1079084A3 (fr) 2002-06-12
DE60012437D1 (de) 2004-09-02
DE60012437T2 (de) 2005-08-04
EP1079084B1 (fr) 2004-07-28
JP2001065330A (ja) 2001-03-13

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